selftests/nolibc: use qemu-system-ppc64 for ppc64le

qemu-system-ppc64 can handle both big and little endian kernels.

While some setups, like Debian, provide a symlink to execute
qemu-system-ppc64 as qemu-system-ppc64le, others, like ArchLinux, do not.

So always use qemu-system-ppc64 directly.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/lkml/20231008-nolibc-qemu-ppc64-v1-1-29e2326e0420@weissschuh.net/Acked-by: Willy Tarreau <w@1wt.eu>

tools/testing/selftests/nolibc/Makefile

@@ -82,7 +82,7 @@ QEMU_ARCH_arm        = arm
 QEMU_ARCH_mips       = mipsel  # works with malta_defconfig
 QEMU_ARCH_ppc        = ppc
 QEMU_ARCH_ppc64      = ppc64
-QEMU_ARCH_ppc64le    = ppc64le
+QEMU_ARCH_ppc64le    = ppc64
 QEMU_ARCH_riscv      = riscv64
 QEMU_ARCH_s390       = s390x
 QEMU_ARCH_loongarch  = loongarch64